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Mack DM

C

CBBC

Member
About 1/2 mike from my farm a guy has a big excavator with a hammer breaking a sandstone hump. Rock is free for the taking so I take the old Mack up there and get him to load up.

Truck has a huge box ... I don't even have wood above the sides, anyway the guy loaded even but full. Pretty much off road so it's ok.

Anyway first hill it's struggling a bit and I missed my down shift, kinda stalled and rolled back but it kept running. But it is chugging and smoke coming out of the air intake. I didn't try to put in gear, just rolled back 20' to flat and set parking break and shut down.

I checked all fluids, all ok. I started back up and ran just fine. I hauled 3 more loads.
I guess it was running backwards? I guess I got lucky. Anything I should watch out for and check?
Thanks. Grant
 
You may want to check the air filter. If they run backwards long enough the exhaust will burn up the paper in the filter.
 
Some old JD two cylinder diesels could run backwards... and blow oil from the air cleaner out the intake! the biggest concern is the oil pump running backwards. You want to shut it off right away, because you have no lubrication.
 
We had a military surplus 6X6 that we was converted to an off road wildfire brush truck. It had a 6 cyl Mack engine and it would run backwards if you stalled it in a similar situation. Would roll backwards and the engine would restart and run backwards. All we did was shut if off and restart it. Never caused any issues with it.
 
That was a common feat back in the '70s when I cut my teeth on the 237 and 300 Maxidyne engines. The old 5 speed transmissions didn't have a low first gear and if you weren't careful with a full load starting off, you could choke it off and refire it, running backwards! I replaced more than one piece of intake/air filter duct work that got melted/burned up. Just make sure all your piping AND the filter are OK and you should be good. The biggest aggravation I had with a DM was inframe overhauls, getting in and out of the cab. Made up a set of steps, took the passenger door and seat off/out for access!!
 
Thanks guys.
I had heard about engines running backwards... but never experienced it. All is well I guess.
Thx. Grant
 
Had a 1070 case that would do that anytime it stalled out. Also done it several times with a cased bore machine in solid rock. It had a deutz motor. I believe the only reason is the valve timing is backwards. Shut it down and fire it back up and it's fine
 
It has a lot to do with the injection pump cam profile. Seen it happen on one of our two cylinder deeres, oil everywhere from the air cleaner, they changed the cam profile on late 720's to keep that from happening.
 
Detroit 6-71 engine would do the same thing. Lug it down until it quits and then the drive train would wind the engine backward. The drivers would call in saying smoke was coming out of the air cleaner.

I always told the drivers the next time it happens to floor the foot pedal until the engine quits. (no oil pressure) Haha. Gutless engines hauling 10 yards of concrete. The only way to drive them was to open the driver's door in the morning and slam it shut on your hand. Then drive it all day like you were ------ off at it!

When they first started making Mack trucks they should have stopped at two. They should have hoisted the first one up and dropped it on the second one.
 
A 5Star Moline diesel with PSB pump will run backwards too. I know I have one and if lug down to far it will restart on own running backwards.
 
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